Hi to all

I have noticed that some of you use a kind of markup to highlight
special passages in emails, for example for Lisp code examples or
for quotes from a manual.

Sometimes I see Lisp code passages displayed with green background
color, sometimes I see quotations enclosed by a frame similar to this:

 _
/
| Text
| Text
| Text
\_

How to do that? Is it a special package or a standard function of Gnus
or Message mode I have not yet discovered? I have searched the net and
the Gnus manual, but I seem to have missed the relevant keywords.

Greetings

Sven